1. Field of the Invention
The present invention relates to an apparatus for correcting aberrations of the human eye, and a method relating to manufacturing the same. More particularly, the invention relates to a wavefront aberrator adapted to be placed on a human eye for correction of higher order aberrations.
2. Description of the Related Art
In traditional optical systems having reflecting and refracting surfaces, it is common to assume that the light passing through the system is limited to paraxial rays, specifically, rays that are near the optical axis and are sustained within small angles. However, practical optical systems rarely are limited to paraxial rays, and thus, the actual images assumed by gaussian optics often depart from the “perfect” image. This departure from the “perfect” image results in the introduction of distortion into the optical system, called aberrations. These aberrations are most problematic in small focal ratio optical systems where the angle from the optical axis is larger.
In a monochromatic optical system with only spherical surfaces, there are five (5) basic ray and wave aberrations, namely, spherical aberrations, coma, astigmatism, curvature of field, and distortion. Optical systems for use with multichromatic light have an additional source of distortion, namely, chromatic aberration.
Because the distortion introduced by aberrations into an optical system significantly degrades the quality of the images on the image plane of such system, there are significant advantages to the reduction of those aberrations. Various techniques are often used to minimize the aberrations. For example, in order to minimize spherical aberrations or coma, a lens may be “bent” to have different radii of curvature on opposite sides while maintaining a constant focal length, such as is contemplated by using the Coddington shape factor. Also, a pair of lenses, where one glass lens has a positive focal length, and the other made from a different glass has a negative focal length, are used together to correct spherical aberration. One example of this technique is the “doublet” lens in which the two lenses have the same radius of curvature on the facing sides, and are cemented together.
Despite the available techniques to minimize the various aberrations, it is often difficult to simultaneously minimize all aberrations. In fact, corrections to an optical system to minimize one type of aberration may result in the increase in one of the other aberrations. This is particularly troublesome when analyzing the human eye as an optical system.
The human eye, namely the cornea and lens, can exhibit a variety of aberrations that diminish the optical performance of the eye resulting in blurred vision. Historically, the optical aberrations have been corrected by introducing man made lenses such as spectacle or contact lenses in front of the human vision system. More recently, more permanent corrections have been made by surgical procedures and techniques such as intraocular lens insertion and corneal sculpting such as Radial Keratotomy, Astigmatic Keratotomy, Automated Lamellar Keratoplasty, Photo Refractive Keratectomy, or Laser In Situ Keratomileuis (LASIK).
The correction of blurred vision by lenses has typically been limited to correction of low order aberrations only, such as defocus and astigmatism. Traditionally, higher order aberrations, e.g., those describable with Zernike polynomials of the third order or higher, could not be corrected using lenses. In addition, due to lens manufacturing limitations and expenses, defocus and astigmatism are typically only corrected in discrete steps, with any correction being made to the nearest one quarter (¼) diopter. Unfortunately, the resolution of one quarter (¼) diopter results in incomplete vision corrections and limits the performance of the patients eye. An advantage of man-made lenses is that any continuing degradation in eye performance can be compensated with by a new lens derived from a current optical examination.
Surgical procedures and techniques provide a more permanent vision correction than non-surgical approaches. Intraocular lenses are man-made lenses that are surgically inserted to replace the defective lens. Corneal sculpting entails various surgical procedures for the modification and alteration of the cornea. The advantage of surgical procedures is that they provide the opportunity for finer resolution corrections. However, any shift in the optical performance of the eye due to aging or trauma requires additional surgeries for corrections or the addition of man-made lenses. Also inherent in all surgical procedures is the risk of infection and permanent damage causing a further degradation in vision.
Consequently, a need exists for an optical element that will precisely compensate for optical aberrations, in addition to defocus and astigmatism, in human vision. This optical element must be easily replaceable as eye performance degrades with age or other defects. Thus, the optical correcting device must be incorporated into the human vision system in a non-invasive and repeatable manner.